I am planning to use multiple Sure Electronics TK2050 2 x 100W boards each connected to an apple airport express and a set of speakers to create a multi room audio system. I am currently running a board off an old printer power supply as a test system but want to buy a more long term solution.

Most of the time the boards will be powering background music. Therefore, what power supply should I get, the speakers will be max 100W, probably going to go with some 65W ones. I am also not an expert on sound. What power supply must I buy so that the system will work correctly? Also, how many boards can one power supply handle or should I only use one power supply per board?

If you want 100W into each speaker then you'll need a power supply capable of supplying that 100W per speaker, so 1 board 2x100W speakers 200W power supply, 2 boards 400W power supply and etc. And the voltage needs to be 32V; any lower and you won't get the 100W per speaker.

Well obviously a 24V 5A power supply won't be enough for 2 x 100W sustained output as it's only able to output 120W with real music it should be ok though.

However, it will only output 100W @ 24V if the impedance of the speakers is 3 Ohms or less, and even then it's at 10% distortion. The speakers has to be 2 Ohms or less for the amp to output 100W @ 0.1% or less distortion.

I'm using it with 4ohm 60W 90db speakers, seems to be a fairly good match.

Yeah, that's pretty much perfect. The amp will output max 60W into 4 Ohms per channel with 24V, and the PS is able to output max 120W totals.

What I don't get is how most people think that a Sure board will output 2 (or 4) x 100W on a 12V battery. It won't ever do that as short circuit protection will kick in before the impedance gets low enough for that (0.56 Ohms total including cable resistance)

What I don't get is how most people think that a Sure board will output 2 (or 4) x 100W on a 12V battery. It won't ever do that as short circuit protection will kick in before the impedance gets low enough for that (0.56 Ohms total including cable resistance)

or worse still, the chip burns out before the short circuit protection kicks in.